This invention relates in general to semiconductor electromechanical devices, and in particular to a microvalve device having a pilot valve.
MEMS (MicroElectroMechanical Systems) is a class of systems that are physically small, having features with sizes in the micrometer range. These systems have both electrical and mechanical components. The term xe2x80x9cmicromachiningxe2x80x9d is commonly understood to mean the production of three-dimensional structures and moving parts of MEMS devices. MEMS originally used modified integrated circuit (computer chip) fabrication techniques (such as chemical etching) and materials (such as silicon semiconductor material) to micromachine these very small mechanical devices. Today there are many more micromachining techniques and materials available. The term xe2x80x9cmicrovalvexe2x80x9d as used in this application means a valve having features with sizes in the micrometer range, and thus by definition is at least partially formed by micromachining. The term xe2x80x9cmicrovalve devicexe2x80x9d as used in this application means a device that includes a microvalve, and that may include other components. It should be noted that if components other than a microvalve are included in the microvalve device, these other components may be micromachined components or standard sized (larger) components.
Various microvalve devices have been proposed for controlling fluid flow within a fluid circuit. A typical microvalve device includes a displaceable member or valve movably supported by a body and operatively coupled to an actuator for movement between a closed position and a fully open position. When placed in the closed position, the valve blocks or closes a first fluid port that is placed in fluid communication with a second fluid port, thereby preventing fluid from flowing between the fluid ports. When the valve moves from the closed position to the fully open position, fluid is increasingly allowed to flow between the fluid ports.
A typical valve consists of a beam resiliently supported by the body at one end. In operation, the actuator forces the beam to bend about the supported end of the beam. In order to bend the beam, the actuator must generate a force sufficient to overcome the spring force associated with the beam. As a general rule, the output force required by the actuator to bend or displace the beam increases as the displacement requirement of the beam increases.
In addition to generating a force sufficient to overcome the spring force associated with the beam, the actuator must generate a force capable of overcoming the fluid flow forces acting on the beam that oppose the intended displacement of the beam. These fluid flow forces generally increase as the flow rate through the fluid ports increases.
As such, the output force requirement of the actuator and in turn the size of the actuator and the power required to drive the actuator generally must increase as the displacement requirement of the beam increases and/or as the flow rate requirement through the fluid ports increases.
Accordingly, there is a need for a microvalve device capable of controlling relatively large flow rates and/or having a displaceable member capable of relatively large displacements with a relatively compact and low powered actuator.
The invention relates to a microvalve device for controlling fluid flow in a fluid circuit. The microvalve device comprises a body having a cavity formed therein. The body further has first and second pilot ports placed in fluid communication with the cavity. The body also has first and second primary ports placed in fluid communication with the cavity. Each port is adapted for connection with a designated fluid source. In a preferred embodiment, one of the pilot ports and one of the primary ports may be in communication with a common fluid source. A pilot valve supported by the body is movably disposed in the cavity for opening and closing the first and second pilot ports. An actuator is operably coupled to the pilot valve for moving the pilot valve. A microvalve is positioned by the fluid controlled by the pilot valve. The microvalve is a slider valve having a first end and a second end. The slider valve is movably disposed in the cavity for movement between a first position and a second position. The first end of the slider valve is in fluid communication with the first and second pilot ports when the first and second pilot ports are open. The second end of the slider valve is in constant fluid communication with the first primary port. When moving between the first and second positions, the slider valve at least partially blocks and unblocks the second primary port for the purpose of variably restricting fluid flow between the primary ports.
In operation, the actuator controls the placement of the pilot valve. In turn, the placement of the pilot valve controls the fluid pressure acting on the first end of the slider valve. The difference between the fluid forces acting on the ends of the slider valve in turn controls the placement of the slider valve. The placement of the slider valve then controls the degree of fluid flow between the primary ports.
The force required to actuate the pilot valve is relatively small. Consequently, the actuator can be relatively compact with relatively low power requirements. Furthermore, the displacement of the slider valve and the flow rate between the primary ports can be relatively large because the fluid force differential associated with the fluid pressures of the fluid sources acting on the ends of the slider valve can be relatively large.